The invention relates to a system having a signal converter device, in one embodiment, an ADC (analog-to-digital converter), and a method for operating a system having a signal converter device.
Conventional microcontroller or microprocessor systems include one or several CPUs (central processing units). The CPU(s) are connected to one or several memories, e.g., a program memory, and a data memory, etc.
The memories may be provided on the same chip, as the CPU(s) (“embedded” microcontroller or microprocessor system), or alternatively separately from the CPU(s).
The program memory e.g., may store the sequence of instructions to be executed by the CPU(s)—i.e., the program—, and the data memory e.g., respective variables, e.g., variables to be changed by the CPU(s) when executing the program.
In addition, conventional microcontroller or microprocessor systems often include one or several signal converter devices, e.g., ADCs (analog-to-digital converters).
By use of an ADC, a continuous input signal, e.g., an analog measuring voltage, a respective current signal, etc., can be converted into a digital number. The digital number then e.g., might be processed by the CPU(s).
The number of different digital numbers an ADC can produce for the allowed range of a continuous input signal is called the “resolution” of the ADC. For example, an ADC that encodes an analog measuring voltage into one of 256 different digital numbers (0 . . . 255) has a resolution of eight bits, since 28=256.
As the input signal is continuous in time, it is necessary to define the rate at which new digital numbers/new discrete values are to be sampled from the input signal. The rate of new values is called the “sampling rate” or “sampling frequency” of the ADC.
ADCs may operate in accordance with a plurality of different converting methods, e.g., the parallel method, the successive approximation method, etc. (or also mixed forms thereof).
In the case of the parallel method, the input signal, e.g., the respective measuring voltage is, by using corresponding comparators, simultaneously compared with n different reference voltages, and it is detected between which two reference voltages the measuring voltage ranges. This way, the digital number pertaining to the input signal may be determined in one single step.
In the case of the successive approximation method, other than with the parallel method, the digital number pertaining to the input signal may not be determined in one single step, but in several processes, wherein only one respective position of the corresponding digital number may be determined per step.
To carry out the above conversion, a C-network, e.g., a network including a plurality of capacitors might be used.
Further, conventional ADCs may include several different input channels via which the input signals, e.g., the respective measuring voltages to be converted are supplied to the ADC.
Before carrying out the above actual conversion (“conversion phase”), a “sample phase” takes place, where the C-network is connected via one of several switches/a respective multiplexer to the respective input channel to be sampled.
During the sample phase, the C-network is loaded from e.g., 0V to the respective measuring voltage present at the respective selected input channel. The measuring voltage e.g., may be provided by a respective sensor connected to the respective input channel.
Afterwards, the C-network is again disconnected from the input channel, and the actual conversion is carried out.
In order to minimize the time needed to load the C-network to the measuring voltage, i.e., to make the sample phase as short as possible, the C-network before starting of the sample phase may be precharged, e.g., to a voltage in the middle of the expected measuring range. During the sample phase, the C-network then only needs to be loaded from the precharge voltage to the respective measuring voltage present at the respective selected input channel.
When the result of the conversion, i.e., the digital number provided by the ADC during the above actual conversion phase is outside the measuring range of the sensor providing the above measuring voltage, an error may be detected (e.g., an error due to broken wires or bad soldering connections between the respective input channel of the ADC, and the sensor).
If such an error detection is desirable, it may be advantageous to completely discharge the C-network prior to the sample phase. For this purpose, an additional switch may be provided across the C-network, which is closed, i.e., brought into an electrically conductive state to discharge the C-network prior to the sample phase, and then opened again, i.e., again brought into a non-conductive state. However, the location of the additional switch directly across the C-network might lead to undesired leakage currents, adversely influencing the accuracy of the actual conversion.
For these or other reasons, there is a need for the present invention.